Role Glycoprotein Shdding from Mammary Carcinoma Cells in the Spread of Metastasis -- DCBD-001, June 1, 1975. (CREG). The main objective of this proposed study is the investigation of plasma membrane glycoconjugates of human mammary tumor cells maintained in tissue culture and transplanted in athymic nude mice. Plasma membrane glycoconjugates will be specifically radiolabeled with tritium by a number of biochemical techniques. The degree of surface labeling as well as its metabolic fate will be monitored by electron microscope autoradiography. Internalization and reutilization of labeled cell surface material will be assessed with this morphological technique while plasma membrane shedding will be quantitated by use of scintillation counting methods. Intact and shed cell surface material will be characterized by use of sodium dodecylsulfate polyacrylamide slab gel electrophoresis. Shedding of mammary cell surface sialyltransferase, an enzyme elevated in the serum of breast cancer patients, will also be monitored in nude mice bearing transplantable human mammary tumors. Isolation, purification and characterization of human serum sialyltransferase is proposed as well as the histochemical localization and characterization of tumor membrane-bound sialyltransferase. These studies should aid in identification of the tissue source and physiological function of the increased sialyltransferase observed in the sera of cancer patients.